Apparatus for removing sulfur dioxide from stack gases

ABSTRACT

A method and apparatus for removing sulfur dioxide from stack gases wherein the stack gas is first subjected to electrically charged water droplets and subsequently to ultraviolet light.

Unite States aient Lauer 5] July 11, 1972 [54] APPARATUS FOR REMOVINGSULFUR [56] References Cited DIOXIDE ST CK G FROM A ASES UNITED STATESPATENTS 72 Inventor: ames L. Lauer c 0 Sun Oil C m an l 1 Box Hook 2, 2y 3,389,971 6/1968 Ailiger ..204/157.1 R

[ Filed: P 1970 Primary Examiner-Howard S. Williams [21] APPL 75 741AltorneyGeorge L. Church, Donald R. Johnson, Wilmer E. McCorquodale, Jr.and Warren L. Soflian Related US. Application Data [62] Division of Ser.No. 765,151, Oct. 4, 1968, Pat. No. [57] ABS CT A method and apparatusfor removing sulfur dioxide from stack gases wherein the stack gas isfirst subjected to electri [52] US. Cl ...204/193 ll h d wat r dr l tand subsequently to ultraviolet [51] Int. Cl. ..B0lj 1/10 fi ht [58]Field ofSearch ..204/l93;23/277 5 Claims, 3 Drawing Figures EPARATOR L 344 32 IB SULFUR PETENTEDJUL 1 1 m2 SHEET 1 OF 2 SULFUR AIR AIR

DC. POWER SUPPLY FIGURE PATENTEDJuL 11 m2 3,676,131 8 SHEET 2 SF 2FIGURE IB APPARATUS FOR REMOVING SULFUR DIOXIDE FROM STACK GASES CROSSREFERENCE TO RELATED APPLICATION This is a division of application Ser.No. 765 ,l5l, filed Oct. 4, 1968, now U.S. Pat. No. 3,565,777.

This invention relates to an improved process and apparatus for cleaninggas, and more particularly relates to the removal of sulfur dioxide fromstack gases.

The contamination or pollution of our air by sulfur dioxide is awell-recognized problem today. The contaminant, sulfur dioxide, isgenerally formed during the combustion of high sulfur-containing fuelssuch as coal or residual fuel oils. Part of the problem can be overcomeby the employment of low sulfur-containing fuels, particularly in theformation of residual fuels; however, since no economical way has beenfound to desulfurize coal, the solution of this problem has had to beovercome by a difierent method. Specifically, these sulfur compoundshave to be removed from the flue gases. Additionally, some of the sulfurdioxide contained in residual fuels can also be removed by stack-gasremoval processes.

Accordingly, over the years many patents have issued and processes havedeveloped for the removal of from stack gases. Examples of such patentsand processes are U. S. Pat. Nos. 2,992,884 and 3,079,223 which employsolid adsorbents; 2,994,585 3,260,035, and 3,047,364 which employ liquidadsorbents; and 3,087,790 and 2,772,315 which reduce the sulfur dioxideto sulfur. Although many of these methods have been triedexperimentally, none appears to be self-supporting in today's marketprimarily due to the high capital cost involved.

It has now been discovered that substantial quantities of sulfur dioxidecan be removed from stack gases by first subjecting the gas toelectrostatically charged droplets of water and subsequently passing thegas through a region illuminated by actinic light. The contaminated gasis subjected to electrostatically charged water droplets because it hasbeen found that considerably more SO can be absorbed by a water spraycontaining charged droplets than can be dissolved in uncharged water.This is based on Onsagers principle, according to which the dissociationconstant of a weak acid is increased in proportion to the electric fieldstrength applied and decreased in inverse proportionality to thedielectric constant. A small charged water droplet is subject totremendous electric fields, and hence a greater amount of S0 will absorbthereon.

The electrostatic droplets are produced by having within the employedpassage means, but substantially outside the path of the gas, a liquidspray chamber having therein liquid spray heads. Water is supplied tothe spray heads, and water droplets are emitted therefrom and subjectedto electrostatic ionizing means. The ionizing means which are locatedbetween the spray heads and the gas flow path consist of alternatelyspaced discharging and non-discharging electrodes. The spacial pathsbetween electrodes are rendered electrically non-conductive by means ofelectrical insulation applied at the exterior surface of thenon-discharging electrodes. When the electrical insulating material isapplied to the exterior surface of the non-discharging electrodes of theionizing means, it aids in the prevention of voltage breakdown in thespacial path between the discharging and non-discharging electrodes.Although the power supply is not critical, generally direct current inthe voltage range of 10,000 to 20,000 volts is preferred. The electricalcharging means can be of any form well known in the art, such asdisclosed in U. S. Pat. Nos. 2,864,458 2,949,168, and 3,331,192.

The second principle involved herein is that when S0 and H 0 aresubjected to intense actinic light, such as ultraviolet light, aphotochemical reaction will take place. The water will be ionized andthe hydrogen ions will react with the sulfur dioxide to liberate freesulfur in crystalline form. The sulfur can then be separated from thegas by methods well known in the art. Although the gas can be subject tocontinuous exposure to ultraviolet light, it is preferable in order toprevent the occurrence of side reactions that intense flash irridiationwith only a few milliseconds lapse be employed when exposing the gas tothe photochemical energy. At least 2,400 joules of energy are requiredper flash at a partial pressure of about 200 mm. of mercury of S0, tocomplete the desired reaction effectively. While a greater amount ofenergy can be applied per flash, conversions are not proportionatelyincreased with the application of additional photochemical energy. As aresult, equipment which provides an energy output of 2,400 to 3,600joules is suitable for this process when operating at a pressure ofabout 200 mm. of mercury. A discussion of the basic reaction mechanismis discussed in The Photochemical Decomposition of Gaseous SulphurDioxide," by R. A. Hill, Trans. Faraday Soc., 1924.

It should be noted that the energy required is directly proportional tothe partial pressure of the gas; thus if the partial pressure of the gasfalls below 200 mm. of mercury of S0 then less energy is required. Forexample, when operating at a pressure of about 10 mm. of mercurypressure, only about joules of energy are required; whereas if theoperating pressure is about 1,000 mm. of mercury, then about 50,000joules of energy are required. As aforementioned, it is preferred thatthe gas be subjected to multiple flashes rather than a continuousirridiation with ultraviolet light. As such, the flash emitting therequired amount of photochemical energy should last for a period of from2 to 4 milliseconds. Other features and embodiments of the instantinvention, in addition to those heretofore recited, will become apparentfrom the accompanying drawings which diagrammatically show the essentialnovel elements of the invention.

In the drawings:

FIG. 1 is a view showing an illustrative embodiment of the inventionwith portions shown in diagrammatic and/or schematic form;

FIG. 1A is a view of a form of the invention shown in F IG. 1, taken inthe direction of the arrows 1A-1A in FIG. 1;

FIG. 1B is a view of a form of the invention shown in FIG. 1, taken inthe direction of the arrows lB-1B in FIG. 1. Referring to FIG. 1,apparatus for removing sulfur dioxide from stack gas is shown as beingcomposed of four sections generally designated as 11, 12, 13, and 14.Sections 11 and 12 are of an electrical insulating material such asphenolic, treated masonite, or any other similar insulating material andare surrounded by an electrically grounded metallic shield 15, which isspaced from said sections by electrical insulators 25. Section 14 is ofmetal and is electrically grounded.

The contaminated stack gas passes into section 11 via opening in inletportion 16 which can be an integral part of the stack gas or a draw-offline. The gas may be forced through the sections by the gas pressure atthe input opening 16 or drawn through by mechanical fans 29 located insection 4. The gas comes into intimate contact in the intermediatemixing zone 50 of section 11 with liquid spray emitted from spray heads17 located in spray chamber section 12. Spray heads 17 are suppliedspray liquid from an external source 18 at some pressure in theneighborhood of 30 to several hundred pounds per square inch dependingon the type of spray heads used.

As the liquid spray passes through section 12, it encounters electricalcharging means consisting of fine wires 19 spaced between metallicelectrodes 20 which are provided with electrical insulation 21 towithstand a working voltage of 20,000 volts DC. or more. The electrodes20 are electrically connected together and grounded externally of theenclosure as indicated in sectional view lA-lA. The insulating andgrounding arrangement is provided in order to preclude electricalflashovers between fine wires 19 and electrodes 20 when a high enoughvoltage is used to provide a strong electrostatic field between finewires 19 and electrodes 20.

The fine wires 19 are given an electrical charge of approximately 10,000to 20,000 volts D.C. above ground potential by power supply 22 whichvoltage is applied through insulator 23. Resistor 24 is provided tolimit the current in case of a short circuit between wires 19 andelectrodes 20. The insulating material 21 is also preferably treatedwith a silicone-type paint to prevent the collection of charged sprayparticles on the insulation. As aforementioned, when the charged spraycomes in contact with the sulfur dioxide, it will absorb thereon. Anyliquid spray which is condensed in section 11 is drained away through adrain pipe. The preferred arrangement which is shown is designed toprevent flashover to ground which would occur if the liquid were drainedaway in a continuous stream. The system is well known in the art andcomprises a metal disc 26 provided with a number of holes to produce adripping action in the chamber enclosed by insulating material 27. Theliquid drips into the chamber and then out drain pipe 28.

The gas and the dissolved SO then pass through the output portion 51into the photochemical reaction zone generally designated as 13.Basically, the zone consists of an input portion generally designated as52, a quartz tube reactor 29 surrounded by a xenon-filled helicalphotoflash lamp 30, and an outlet portion 53. The flash lamp hastungsten electrodes 31 and a trigger electrode 32. The quartz isconnected to sections 11 and 14 via fittings 33. Four condenser banks inparallel at 34 supply the discharge current. Each condenser bankcontains four parallel-connected condensers of microfarads each so thatthe total capacity is 400 microfarads. Generally, at least 300microfarads are necessary and 300 to 500 microfarads is a suitablerange. Power supply 35 supplies sufficient direct current voltage toobtain a maximum condenser voltage of 4,000 volts and charges at ratesup to 10 milliamperes. Shunt resistor 36 provides for bleeding offresidual condenser charge after the lamp has been fired. The triggercircuit consists of the coil 37 capable of generating up to 10,000 voltsin the secondary when the battery 38 is charged. Three-tenths microfaradcondenser 39 is discharged through the switch 40 in the primary. Thelamp is enclosed by an aluminum reflector 41 as indicated in sectionalview 18-18, and dry air is blown through the space via line 42 betweenthe reaction zone and the helix to keep the latter cool. In calibration,uranyl oxalate actinometry is used to measure the light output of eachlamp flash, and flash duration is measured with an oscilloscope. Itshould be noted that the circuitry as aforedescribed is well known andstandard in the art, and various modifications thereto which do notdeter the activation of the UV lamps would be operable.

Following the photochemical reaction, the gas and sulfur particles passinto a separator. The separator can be any apparatus well known in theart for separating solid material from a gas, Examples of such apparatusare cyclone separators, filter screens, baffle plates, and the like. Thegas is separated and leaves via line 45 while the sulfur and possiblyany other particulate material present leave through line 44.

As a secondary embodiment of the instant invention, the helical sourceof ultraviolet light as depicted in FIG. 1 could be replaced by a lampbank of high intensity mercury lamps. The bulbs would be connected inseries in order to flash simultaneously. Also, a simple drain systemcould be employed in the mixing section rather than the flashoverpreventive type as aforedescribed.

As a further embodiment of the invention, particulate materials such asdust particles, fly ash, metal contaminants, etc., can be removed fromthe stack gas along with the sulfur dioxide by employing the methods asset forth in U. S. Pat. Nos. 2,357,355 and 3,331,192 which employsimilar apparatus. As disclosed therein, the gas upon entrance into themixing zone is subjected to an electric field which gives anelectrostatic charge to the particulate material opposite to that of thewater droplets. The charged droplets and the charged particulatematerial then are attracted to each other and are thereafter separatedusing baffle plates. In a like manner, a gas containing both particulatematerials and sulfur dioxide can upon entrance into the mixing zone besubjected to an electric field. The electrostatically chargedparticulate material and the sulfur dioxide would then contact thecharged water droplets as aforedescribed, and subsequently be removedfrom the gas by baffle plates and photochemical reaction, respectively.eferably, the sulfur dioxide would be removed first so that a maximumamount of sulfur could be fonned.

As will be well recognized by one skilled in the art, the embodiments ofthe invention as specifically described and illustrated herein areexemplary of the preferred modes of operation, and variousmodifications, such as vertical positioning of the apparatus, changingelectrical connections, etc., can be made thereto without departing fromthe scope of the invention as defined in the claims.

I claim:

1. An apparatus for removing sulfur dioxide from a gas comprising:

a. passage means for transmitting a gas therethrough;

b. spray input means located in said passage means at a position outsidethe path of flow of the gas passing through said passage means fordisseminating a liquid spray into said passage means;

0. ionizing means cooperable with respect to said spray input means andliquid spray for ionizing droplets of said liquid spray prior todissemination thereof in said passage means; and

d. photochemical reaction means located outside said passage means andcooperable therewith for inducing a photochemical reaction upon thepassage of the gas therethrough subsequent to the contacting of the gaswith said ionized droplets for producing sulfur from sulfur dioxidecarrying water droplets.

2. An apparatus as described in claim 1 wherein a. said passage meansconsists of an inlet portion and intermediate mixing portion and anoutput portion; and

b. including spray chamber means laterally displaced from and connectedto said intermediate mixing portion wherein said spray input means arepositioned.

3. An apparatus as described in claim 2 wherein a. said ionizing meanscomprises discharging electrode means, non-discharging electrode meanscooperably spaced with respect to said discharging electrode means todefine spraypassage space therebetween, said nondischarging electrodemeans being coated with insulating material, and an electric powersupply cooperable to apply unidirectional electric potential betweensaid discharging electrode means and said non-discharging electrodemeans and across said spray-passage space and the particles of liquidspray moving therethrough; and

b. said photochemical reaction means is cooperable with the outputportion of said gas passage means and comprises an inlet portion, anintermediate reaction portion, and an outlet portion, wherein saidintermediate reaction portion comprises a quartz reaction zone, anultraviolet light source surrounding said quartz reaction zone forinducing the photochemical reaction therein upon passage of the gastherethrough, and electrical means for activating said ultravioletsource.

4. An apparatus as described in claim 3 including means connected tosaid output portion of the photochemical reaction means for separatingthe sulfur from the gas stream as it passes therethrough.

5. An apparatus as described in claim 3 wherein said ultraviolet sourceis a helical lamp surrounding said quartz reaction zone.

2. An apparatus as described in claim 1 wherein a. said passage meansconsists of an inlet portion and intermediate mixing portion and anoutput portion; and b. including spray chamber means laterally displacedfrom and connected to said intermediate mixing portion wherein saidspray input means are positioned.
 3. An apparatus as described in claim2 wherein a. said ionizing means comprises discharging electrode means,non-discharging electrode means cooperably spaced with respect to saiddischarging electrode means to define spray-passage space therebetween,said non-discharging electrode means being coated with insulatingmaterial, and an electric power supply cooperable to applyunidirectional electric potential between said discharging electrodemeans aNd said non-discharging electrode means and across saidspray-passage space and the particles of liquid spray movingtherethrough; and b. said photochemical reaction means is cooperablewith the output portion of said gas passage means and comprises an inletportion, an intermediate reaction portion, and an outlet portion,wherein said intermediate reaction portion comprises a quartz reactionzone, an ultraviolet light source surrounding said quartz reaction zonefor inducing the photochemical reaction therein upon passage of the gastherethrough, and electrical means for activating said ultravioletsource.
 4. An apparatus as described in claim 3 including meansconnected to said output portion of the photochemical reaction means forseparating the sulfur from the gas stream as it passes therethrough. 5.An apparatus as described in claim 3 wherein said ultraviolet source isa helical lamp surrounding said quartz reaction zone.